Compatibilized pressure-sensitive adhesives

ABSTRACT

Disclosed is a composite pressure-sensitive adhesive comprising from about 95 to about 5 parts by weight of an acrylic pressure-sensitive adhesive; from about 5 to about 95 parts by weight of an at least partially soluble (in a solvent) polymer, and a compatibilizer present in the composite pressure-sensitive adhesive in an amount greater than 0 to about 10 parts by weight of the composite pressure-sensitive adhesive. The polymer is selected from the group consisting of a butadiene-containing polymer, an isoprene-containing polymer, a saturated olefin-containing polymer, and a styrene-containing polymer. The compatibilizer in the adhesive has a structure selected from the group consisting of (1) an acrylic adhesive-compatible segment and a polymer-compatible segment wherein at least a portion of the compatibilizer is present throughout either the acrylic adhesive, the polymer, or both, and (2) an acrylic adhesive-reactive segment and a polymer-compatible segment wherein at least a portion of the compatibilizer is present throughout the polymer.

TECHNICAL FIELD

This invention relates to multi-component pressure-sensitive adhesives.More specifically, this invention relates to compositepressure-sensitive adhesives containing two main polymer components,which may be present in different layers in a multilayer structure or asa mixture.

BACKGROUND

Pressure-sensitive adhesives are well known in the art for bonding to avariety of materials such as glass, metals, painted surfaces, plastics,and the like. Multilayer films, both with and without pressure sensitiveadhesive layers, have been described as, for example, films having tearor puncture resistance or mirror-like properties, and tapes.Intermediate layers have been described for use in multilayeredconstructions to adhere different polymeric materials that otherwisehave insufficient interlayer adhesion. Intermediate layers, or tielayers, generally have an affinity for both of the principal layers.Blends of otherwise incompatible polymers also have been produced usingcompatiblizers.

DISCLOSURE OF INVENTION

Briefly, the present invention provides a composite pressure-sensitiveadhesive (PSA) comprising from about 95 to about 5 parts by weight of anacrylic pressure-sensitive adhesive; from about 5 to about 95 parts byweight of an at least partially soluble (in a solvent) polymer selectedfrom the group consisting of a butadiene-containing polymer, anisoprene-containing polymer, a saturated olefin-containing polymer, anda styrene-containing polymer; and a compatibilizer present in thecomposite pressure-sensitive adhesive in an amount greater than 0 toabout 10 parts by weight of the composite pressure-sensitive adhesive,the compatibilizer having a structure selected from the group consistingof (1) an acrylic adhesive-compatible segment and a polymer-compatible(i.e., compatible with the polymer of the composite PSA) segment whereinat least a portion of the compatibilizer is present substantiallythroughout either the acrylic adhesive, the polymer, or both, and (2) anacrylic adhesive-reactive segment and a polymer-compatible segmentwherein at least a portion of the compatibilizer is presentsubstantially throughout the polymer.

In this description, “compatible” means that materials form thermallystable non-equilibrium morphologies during processing that do notsignificantly coalesce into separate phases or increase in domain sizeupon aging at temperatures at or above the glass transition temperatures(Tg) or melting transition temperatures (Tm) of the materials.

A “compatible mixture” refers to a material capable of forming adispersion in a continuous matrix of a second material, or capable offorming a co-continuous polymer dispersion of both materials.

“Compatibilizer” means a material comprising less than about 10 weightpercent of at least one phase of a system having two or more phases,that improves the interfacial adhesion between two otherwise immisciblematerial phases. The compatibilizer is present throughout at least onephase, it is preferentially present at an interface between at least twoof the phases, and it increases the compatibility of at least two of thephases in the system. If the weight ratio of the compatibilizer in thesystem is too high relative to the other phases, a portion of it mayseparately form a distinct phase.

“Miscible” as used for a polymer blend, means any blend having a freeenergy of mixing less than zero, and “immiscible” as used for a polymerblend, means any blend having a free energy greater than zero. Amiscible polymer is capable of forming a blend with a second material,which blend appears to be a single phase with no apparent phaseseparation, and such capability may depend on the temperature of theblend.

“Reactive” means that components are capable of forming a chemical bond,which may be covalent or ionic.

“Copolymer” means a block, graft or random copolymer.

“Crosslink” means an element, group, or compound that attaches twochains of polymer molecules, primarily through chemical bonding.

“Continuous” means an uninterrupted phase of a component;“discontinuous” means a discrete phase dispersed within a continuousphase; and “co-continuous” means a multiphase morphology of a dispersionor blend of two or more components, wherein each component in the blendis essentially continuous in nature, and the pattern(s) of one or morephases may be irregular or complex.

The present invention provides improved adhesive properties including180° peel adhesion, cohesive strength, shear strength, and anon-equilibrium morphology that is more thermally stable than similarcompositions without compatibilizer. The present invention also providesimproved interlayer adhesion in multilayer embodiments of the invention.The present invention further provides improved layer stability whenmultilayer embodiments are aged at elevated temperatures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a cross-sectional digital image of a scanning electronmicrograph taken at 1000×magnification showing the morphology of a13-layer composite PSA of the present invention.

FIG. 1(b) is a cross-sectional digital image of a scanning electronmicrograph taken at 1500×magnification of the adhesive shown in FIG.1(a) without compatibilizer.

FIG. 2 is a graph depicting the tensile stress versus strain for twocomposite PSAs of the present invention, along with two adhesiveswithout compatibilizer at 50° C.

FIG. 3 is a graph depicting the tensile stress versus strain of theadhesives shown in FIG. 2, at 100° C.

FIG. 4(a) is a digital image of an optical micrograph taken at250×magnification showing the morphology of a composite PSA of thepresent invention.

FIG. 4(b) is a digital image of an optical micrograph taken at250×magnification showing the morphology of the composite PSA of FIG.4(a) after exposure to 160° C. for one hour.

FIG. 5(a) is a digital image of an optical micrograph taken at250×magnification showing the morphology of an adhesive similar to thatshown in FIGS. 4(a) and 4(b), without compatibilizer.

FIG. 5(b) is a digital image of an optical micrograph taken at250×magnification showing the morphology of the adhesive shown exposureto 160° C. for one hour.

FIG. 6(a) is a cross-sectional digital image of a scanning electronmicrograph taken at 500×magnification showing the morphology of anothercomposite PSA of the present invention.

FIG. 6(b) is a cross-sectional digital image of a scanning electronmicrograph taken at 500×magnification of the adhesive shown in FIG. 6(a)without compatibilizer.

DETAILED DESCRIPTION

Adhesives normally bond by surface attachment to other substances, whichincludes adhesives. A PSA displays permanent and aggressive tackiness toa variety of substrates by applying only light pressure. An acceptedquantitative description of a PSA is given by the Dahiquist criterion(see Handbook of Pressure-Sensitive Adhesive Technology, Second Edition,D. Satas, ed., Van Nostrand Reinhold, New York, N.Y., 1989, pages171-176), which indicates that materials having a storage modulus (G′)of less than about 3×10⁵ Pascals (measured at 10 radians/second at roomtemperature, about 22° C.) have PSA properties, while materials having aG′ above this value do not. More specifically, a PSA as used hereinrefers to a material that has a storage modulus below the Dahlquistcriterion at the use temperature, which may be different than roomtemperature.

The composition of a particular adhesive may be tailored to a selecteduse. To accomplish this, PSAs require a balance of viscous and elasticproperties resulting in a balance of adhesion, cohesion, and elasticity.These properties are measured by known methods, including shear, peel,and tack testing. PSAs generally comprise elastomers that are inherentlytacky, elastomers that are tackified with the addition of tackifyingresins, or thermoplastic elastomers that are tackified with the additionof tackifying resins. PSAs can be blended with solvent, coated, and thesolvent removed, such as by drying at elevated temperatures. PSAs mayalso be coated without using solvents, such as by extrusion processing.For some applications, PSAs can be modified by crosslinking to obtain adesired balance of properties.

Acrylic PSAs generally have a glass transition temperature of about −20°C. or lower. Such acrylic adhesives may comprise from 100 to 80 weightpercent (wt %) of a C₃-C₁₂ alkyl ester component, for example, isooctylacrylate, 2-ethylhexyl acrylate, and n-butyl acrylate, and from 0 to 20wt % of an ethylenically-unsaturated component such as, for example,acrylic acid, methacrylic acid, ethylene vinyl acetate, andN,N-dimethylacrylamide. Preferably, the acrylic PSA comprises from 0 toabout 20 wt % of acrylic acid and from 100 to about 80 wt % of isooctylacrylate. The acrylic PSAs can be polymerized by techniques including,but not limited to, solvent polymerization, emulsion polymerization,suspension polymerization, and solventless bulk polymerization. TheC₃-C₁₂ alkyl ester component and the optional ethylenically-unsaturatedcomponent may also comprise a polymerization initiator, especially athermal initiator or a photoinitiator of a type and in an amounteffective to polymerize the acrylic PSA. The acrylic PSAs may beinherently tacky at the use temperature, or tackified. Useful tackifiersfor acrylics include aliphatic resins, aromatic resins, rosin esters,and terpene resins.

In the present invention, a compatibilizer can have a structureincluding an acrylic adhesive-compatible segment and apolymer-compatible segment that permits the compatibilizer to be blendedinto the acrylic adhesive, the polymer, or both. Alternatively, acompatibilizer can have a structure including an acrylicadhesive-reactive segment and a polymer-compatible segment that allowsthe compatibilizer to be blended into the polymer but not the acrylicadhesive. When the compatibilizer is blended into another component, itis typically present substantially throughout that component. Theconcentration of compatibilizer in the component in which it is blended(a first component) need not be uniform throughout the component, inorder to be present substantially throughout that component (e.g., theconcentration at an interface of the first component with a secondcomponent may be greater than the concentration of the compatibilizer inthe bulk of the first component).

A preferred compatibilizer for the present invention is a compositionhaving the formula R-Y, which may be a copolymer, wherein Y is a segmentselected from the group consisting of a) at least one alkyl(meth)acrylate ester, wherein the alkyl group contains from 1 to about20 carbon atoms, and b) at least one functional group capable ofundergoing an ionic interaction or covalent reaction with the acrylicadhesive component of the composite PSA. R is a segment selected tocorrespond to the polymer in the composite PSA. More specifically, R isa butadiene-containing segment when a butadiene-containing polymer isselected for the adhesive composite. Correspondingly, R is anisoprene-containing segment when an isoprene-containing polymer isselected for the adhesive composite, and R is a styrene-containingsegment when a styrene-containing polymer is selected for the adhesivecomposite.

In the compatibilizer having the formula R-Y, when R is a saturatedolefin-containing segment, Y is a segment having at least one functionalgroup capable of undergoing an ionic interaction or covalent reactionwith the acrylic adhesive component of the composite PSA.

When the chosen compatibilizer is a composition having the formula R-Y,Y is preferably a segment having at least 70 parts of at least onepolymerizable monomer of an alkyl acrylate, alkyl methacrylate, ormixtures thereof, and from greater than 0 to 30 parts of at least onepolar monomer selected from the group consisting of acrylic acid,methacrylic acid, itaconic acid, maleic acid, N-vinyl pyrrolidone,N-vinyl caprolactam, acrylamide, t-butyl acrylamide,N,N-(dimethylamino)ethyl acrylamide, N,N-dimethyl acrylamide,N,N-dimethyl methacrylamide, N-vinylpyridine, and mixtures thereof. Themonomers are polymerizable via an addition mechanism, including anionicand/or free radical mechanisms.

Another preferred Y segment contains at least one functional groupcapable of undergoing an ionic interaction or covalent reaction with theacrylic adhesive component of the composite PSA. When the selectedpolymer is butadiene-containing, isoprene-containing, orstyrene-containing, this functional group is selected from the groupconsisting of carboxylic acid, sulfonic acid, phosphoric acid, hydroxy,lactam, lactone, N-substituted amide, N-substituted amine, anhydride,epoxide, isocyanate, carbamate, and mixtures thereof. When the selectedpolymer is a saturated olefin-containing polymer, this functional groupis an amine selected from the group consisting of 3-dimethylaminopropylamine, N,N-dimethylethylenediamine, 2-(2-aminoethyl)pyridine,1-(2-aminoethyl)pyrrolidine, 3-aminoquinuclidine, and mixtures thereof.

When the composite adhesive includes butadiene-containing polymers, thepreferred compatibilizer is selected from the group consisting ofbutadiene-4-vinylpyridine copolymer, butadiene-isooctyl acrylatecopolymer, butadiene-2-vinylpyridine copolymer, butadiene-isooctylacrylate-acrylic acid copolymer, butadiene-(meth)acrylamide copolymer,butadiene-acrylic acid copolymer, butadiene-N-(3-aminopropyl)methacrylamide copolymer, butadiene-NN-(dimethylamino)ethylacrylate,butadiene-2-diethylaminostyrene copolymer,butadiene-glycidylmethacrylate copolymer,butadiene-2-hydroxyethylmethacrylate copolymer,butadiene-N-vinylpyrrolidone copolymer, and mixtures thereof.

When the composite adhesive includes an isoprene-containing polymer, thepreferred compatibilizer is selected from the group consisting ofisoprene-4-vinylpyridine copolymer, isoprene-isooctyl acrylatecopolymer, isoprene-2-vinylpyridine copolymer, isoprene-isooctylacrylate-acrylic acid copolymer, isoprene-(meth)acrylamide copolymer,isoprene-acrylic acid, isoprene-N-(3-aminopropyl)methacrylamidecopolymer, isoprene-N,N-(dimethylamino)ethylacrylate copolymer,isoprene-2-diethylaminostyrene copolymer, isoprene-glycidylmethacrylatecopolymer, isoprene-2-hydroxyethylmethacrylate copolymer,isoprene-N-vinylpyrrolidone copolymer, and mixtures thereof.

When the composite adhesive includes a saturated olefin-containingpolymer, the preferred compatibilizer is the product of a reactionbetween a polyolefin having an anhydride, epoxide, or acidfunctionality, and an amine selected from the group consisting of3-dimethylaminopropyl amine, N,N-dimethylethylenediamine,2-(2-aminoethyl)pyridine, 1-(2-aminoethylpyrrolidine,3-aminoquinuclidine, and mixtures thereof.

When the composite adhesive includes a styrene-containing polymer, thepreferred compatibilizer is selected from the group consisting ofstyrene-4-vinylpyridine copolymer, styrene-isooctyl acrylate copolymer,styrene-2-vinylpyridine copolymer, styrene-isooctyl acrylate-acrylicacid copolymer, styrene-(meth)acrylamide copolymer, styrene-acrylic acidcopolymer, styrene-N-(3-aminopropyl)methacrylamide copolymer,styrene-N,N-(dimethylamino)ethylacrylate copolymer,styrene-2-diethylaminostyrene copolymer, styrene-glycidylmethacrylatecopolymer, styrene-2-hydroxyethylmethacrylate copolymer,styrene-N-vinylpyrrolidone copolymer, and mixtures thereof.

The preferred level of compatibilizer ranges from greater than 0 toabout 10 parts by weight of the composite pressure-sensitive adhesive.However, when melt-processing is used to produce the composite PSAs ofthe present invention, a more preferred compatibilizer range is 0.1 toabout 2 wt %. As the compatibilizer level in some embodiments of thepresent invention is increased above about 2%, the composite PSA becomesmore difficult to draw down into a thin film.

In some embodiments, a compatibilizer that is not a product of areaction between the acrylic pressure-sensitive adhesive and the polymeris preferred.

The polymer component of the inventive composite PSA may be inherentlytacky at the use temperature, or may be tackified (i.e., the polymer mayitself be a PSA). Useful tackifiers may depend upon the particularpolymer, but generally include aliphatic resins, aliphaticolefin-derived resins, aromatic resins, hydrogenated hydrocarbons,polyaromatics, polyterpenes, rosin esters, terpene phenolic resinsderived from petroleum or terpentine sources, and terpene resins.

The polymer component of this invention is also at least partiallysoluble in a good solvent or cosolvent. That is, at least 1 wt % of thepolymer component dissolves in the solvent, preferably at least 5 wt %,more preferably at least 10 wt %. Most polymer components used in thepresent invention dissolve well beyond these amounts, with manycompletely dissolving. The amount of the polymer component thatdissolves may be determined from known methods. For example, percent gelmethods used in the adhesive art are useful to determine the amount of apolymer that is soluble if it does not completely dissolve. Such amethod is taught in U.S. Pat. No. 5,859,088.

The polymer component of this invention may be partially crosslinked. Inthese cases, a portion of the polymer will still be soluble in a goodsolvent. Some materials may need to be processed before use to improvesolubility or reduce melt viscosity. Isoprene containing systems likenatural rubber are one such example. Because of the high molecularweight (MW) and gel content of some grades of natural rubber, only asmall percentage of the material may be soluble. To improve solubilityin this situation, the MW and gel content may be reduced using knownprocessing techniques.

Some polymers, such as polyolefins, are known to be difficult tosolvate. However, under the right conditions solvation can beaccomplished. For instance, polyethylene will become soluble inchlorobenzene at elevated temperatures (e.g., 100° C.). This is alsowithin the scope of this invention.

It is well known in the art that the extent of gelation for crosslinkedpolymer systems is related to the amount of crosslinking agent utilizedduring a polymerization process. If too much crosslinking agent is usedthe system can form a gel. Typically, this can occur when as little as0.5 parts by weight of crosslinking agent is added to the formulation.In any case, these systems still typically contain a small fraction ofsoluble polymer chains until the crosslinker concentration or crosslinkdensity is high enough to insure that every polymer chain has beenincorporated into the network structure. Common agents that formcrosslinks during the polymerization include di- and multi-functionalmonomeric species (e.g., divinylbenzene, ethyleneglycoldimethacrylate,and trimethylol propane triacrylate). Polymer components of thisinvention may contain crosslinks as long as they retain some degreesolubility in a good solvent. However, this stipulation is only placedon the polymer component before it is processed into a PSA construction.The overall composite PSA of this invention does not need to meet thissolvation criterion.

Butadiene-containing polymers include, for example, styrene-containingcopolymers such as acrylonitrile/styrene andacrylonitrile/butadiene/styrene for example Tyril™ 100 and Magnum AG™700 (from Dow Chemical Co., Midland, Mich. (Dow));styrene-butadiene-styrene block copolymers such as Kraton™ 1118 (fromShell Chemical Co., Houston, Tex. (Shell)); and polybutadiene such asDiene™ 645 (from Firestone Synthetic Rubber & Latex Co., Akron, Ohio).

Isoprene-containing polymers include, for example, linear, radial andstar styrene-isoprene-styrene block copolymers such as Kraton™ 1107(from Shell), synthetic polyisoprenes such as Natsyn™ 2210 (fromGoodyear Tire and Rubber Co., Akron, Ohio) natural rubbers such as CV-60a controlled viscosity grade of rubber, and random copolymer rubberssuch as Ameripol Synpol 1011 A (from Ameripol Synpol Co., Port Neches,Tex.).

Saturated olefin-containing polymers include, for example, polyolefinssuch as isotactic polypropylene, low density polyethylene, linear lowdensity polyethylene, very low density polyethylene, medium densitypolyethylene, high density polyethylene, polybutylene, andnon-elastomeric polyolefins such as ethylene/propylene copolymers andblends thereof, ethylene-vinyl acetate copolymers such as thoseavailable as Elvax™ 260 (from DuPont, Wilmington, Del.);ethylene/poly-α-olefin copolymers such as Engage™ 8200 (from Dow); andlinear, radial, and star styrene-ethylene/butylene-styrene blockcopolymers such as Kraton™ 1657 (from Shell).

Styrene-containing polymers include, for example, linear, radial, andstar styrene-isoprene-styrene, styrene-butadiene-styrene, andstyrene-ethylene/butylene-styrene block copolymers such as Kraton™ 1107,1118, and 1657, respectively (from Shell); polystyrene and high-impactpolystyrene for example Styron™ 615 and 484, respectively, (from Dow);and styrene-containing copolymers. Useful star-block copolymers includethose taught in U.S. Pat. Nos. 5,296,547 and 5,412,031, which are hereinincorporated by reference.

Other materials can be added to the acrylic PSA and/or to the polymer,for special purposes. For example fillers, pigments, antioxidants,ultraviolet light (UV) stabilizers, plasticizers, and crosslinkers orcuring agents may be included in amounts sufficient to achieve thedesired results.

Pigments and fillers can be used in the polymer, acrylic PSA, or both,to modify cohesive strength and stiffness, cold flow, and tack, as wellas chemical resistance and gas permeability. For example, aluminumhydrate, lithopone, whiting, and the coarser carbon blacks such asthermal blacks also increase tack with moderate increase in cohesion.Whereas clays, hydrated silicas, calcium silicates, silico-aluminates,and the fine furnace and thermal blacks increase cohesive strength andstiffness. Platy pigments and fillers, such as mica, graphite, and talc,are preferred for acid and chemical resistance and low gas permeability.Other fillers can include glass or polymeric beads or bubbles, metalparticles, fibers, and the like. Each of these additives is used in anamount sufficient to produce the desired result. Typically, pigments andfillers are used in amounts of about 0.1 to about 20 wt %, based on thetotal weight of the composite PSA.

Antioxidants and/or ultraviolet light (UV) stabilizers may be used toprotect against environmental aging caused by ultraviolet light or heat.These include, for example, hindered phenols, amines, and sulfur andphosphorus hydroxide decomposers. These antioxidants and stabilizers areused in an amount sufficient to produce the desired result. Typically,they are used in amounts of about 0.1 to about 5.0 wt %, based on thetotal weight of the composite PSA.

Plasticizers can be used in the polymer, acrylic PSA, or both to lowerthe modulus and Tg of the material in which plasticizer is mixed. Theycan be used to modify the strength and stiffness, cold flow, and tackproperties.

Crosslinkers such as bis(aziridines) or the equivalent, benzophenone,derivatives of aziridine and benzophenone, and substituted aziridinesand benzophenones such as 1,1-isophtaloyl-bis(2-methylaziridine) oracryloyloxybenzophenone (which has been copolymerized with the acrylateadhesive monomers and then irradiated) may also be added. Suchcrosslinkers may be activated thermally, or with a radiation source,such as UV or electron-beam radiation, preferably after coating thecomposite PSA to the desired thickness. These crosslinkers are used inan amount sufficient to produce the desired result, which is normally anincrease in shear strength. Typically, crosslinkers are used in amountsof about 0.1 to about 5.0 wt %, based on the total weight of thecomposite PSA.

Ultraviolet crosslinkers are preferably activated with long wavelengthUV radiation (280-400 nm). The absorption maximum will depend on themolecular structure of the crosslinking agent. High-intensity and lowintensity UV lights are useful. Such high-intensity UV lights andprocessors are commercially available, for example from PPG, Pittsburgh,Pa. and Fusion UV Systems, Inc., Gaithersburg, Md. Low-intensity UVlights are available as germicidal lamps.

Electron beam radiation may be used to crosslink the composite PSA ofthe present invention. An electron beam apparatus includes an electronbeam source that directs electrons into the material to be crosslinked.The electron beam source may be any electron beam source that emitselectron beam radiation sufficient to achieve a desired degree ofcrosslinking in the particular composite PSA material selected. Thetypical electron beam apparatus provides a dose of 5 to 100 kiloGray(kGy) (0.5 to 10.0 Mrad) with electrons under an accelerating potentialof 30 to 300 kilovolts (kV). Manufacturers of suitable electron beamradiation sources include Energy Sciences Inc., in Wilmington, Mass.,and RPC Industries, in Hayward, Calif.

The composite PSA of the present invention may comprise a layered form,a blend of materials as the overall form, or a layered form wherein oneor more layers comprises a blend of two or more materials.

The materials within the composite PSA of the present invention can haveany one of several types of phase morphologies. The materials may form acontinuous phase; one material may form a discontinuous phase dispersedwithin a continuous phase of another material; and a blend of two ormore of the components may form a co-continuous multiphase morphology,wherein each material in the blend is essentially continuous in nature.The different phase morphologies may be present as an overall blend. Oneor more layers of a layered composite PSA may have the same or differentphase morphology of another material layer. That is, in an AB-layeredcomposite PSA, layer A may have a continuous, discontinuous, orco-continuous morphology, while layer B may independently have acontinuous, discontinuous, or co-continuous morphology.

These composite PSAs are prepared by melt processing (e.g., extruding)or by solvent casting. The materials used to prepare the composite PSAsof the present invention are melt processable when they are fluid orpumpable, and they do not significantly degrade or gel at thetemperatures used to melt process (e.g., extruding or compounding) thecomposite PSA (e.g., about 50° C. to about 300° C.). Preferably, suchmaterials have a melt viscosity of about 10 poise to about 1,000,000poise, as measured by capillary melt rheometry at the processingtemperatures and shear rates employed in extrusion. Typically, suitablematerials possess a melt viscosity within this range at a temperature ofabout 175 to 225° C. and a shear rate of about 100 seconds⁻¹.

Melt processing is the preferred method for the layered form of thisinvention. The layers are generally formed at the same time while in amolten state, and then cooled. Preferably, the layers are substantiallysimultaneously melt-processed, and more preferably, the layers aresubstantially simultaneously co-extruded. Preferably, the totalthickness of all the layers is no greater than about 250 μm thick (morepreferably, no greater than about 150 μm, and most preferably, nogreater than about 50 μm). Such layered composite PSAs have aconstruction of at least 2 layers (preferably at least 5 layers) toabout 100 layers. More preferably, layered composite PSAs have at least13 layers. Depending on the materials and any additives chosen, layerthickness, and processing parameters used, for example, the layeredcomposite PSAs will typically have different properties at differentnumbers of layers. That is, the same property (e.g., peel adhesion,shear strength, tensile strength) may go through maximum at a differentnumber of layers for a particular set of materials when compared toanother set of materials. Any crosslinking agent used must be stable atthe temperatures used to melt process the composite PSA. Preferredcrosslinking processes for melt-processed composite PSAs includeelectron beam and UV methods.

Layered composite PSAs can include an (AB)_(n) form, with either Aand/or B layers as the outermost layers (e.g., (AB)_(n)A, (BA)_(n)B, or(AB)_(n)), and preferred layered forms include A(BA)₅BA andACBC(ACBC)₅A. In such forms, A, B and C (if present) are layers ofdifferent polymers, at least one of which is a PSA, provided that atleast one outermost layer is a PSA, and at least one of which layersincludes a compatibilizer present substantially throughout the layer. Ineach of these forms, n is preferably at least 2, and more preferably, atleast 5, and is selected depending on the materials used and theapplication desired. A lower number of layers may be preferred for oneset of materials while a higher number of layers is preferred foranother set of materials.

A lower number of layers is often preferred for a microlayer compositePSA that is difficult to coextrude. Interfacial instabilities can occurat the interfaces when the microlayer composite PSA is being coextruded,which leads to an irregular surface and probably layer breakup. In thesecases, a fewer number of layers provides less opportunity forinterfacial instabilities and more stable coextrusion. A higher numberof layers is preferred for microlayer composite PSA systems where astiff thermoplastic is a component in the construction. By increasingthe number of layers in the construction, the thickness of eachindividual layer is reduced, which imparts ductility to the stiffpolymer. This provides improved compliance and higher adhesion for thecomposite PSA.

The present invention allows one to incorporate otherwise incompatiblematerials in a small number of layers. For example, when acompatibilizer is blended into one or more layers of a five-layercomposite PSA, each layer can contribute properties to the overallconstruction without the need for devoting two layers to separate tielayer compositions. This advantage greatly increases the flexibility inmaterial selection with only five layers.

When the number of layers is increased, such as with more than 10layers, the adhesive component can have much greater interfacial contactwith layers of other materials to reduce delamination between layers.Surprisingly, the composite PSA of the present invention can provideadvantages of higher shear strength without compromising peel adhesion,and also have improved thermal stability when the compatibilizer is usedin a multilayer PSA. As the number of layers is increased, the overallthickness of the composite PSA may or may not be increased.

Layered composite PSAs of the present invention can be made using avariety of equipment and a number of melt-processing techniques(typically, extrusion techniques) well known in the art. Such equipmentand techniques are disclosed, for example, in U.S. Pat. No. 3,565,985(Schrenk et al.), U.S. Pat. No. 5,427,842 (Bland et al.), U.S. Pat. No.5,599,602 (Leonard et al.), and U.S. Pat. No. 5,660,922 (Herridge etal.). For example, single- or multi-manifold dies, full moon feedblocks(such as those described in U.S. Pat. No. 5,389,324 to Lewis et al.), orother types of melt processing equipment can be used, depending on thenumber of layers desired and the types of materials extruded. Forextruding pressure sensitive adhesives, for example, slab feed extrudersare typically used.

For example, one technique for manufacturing layered composite PSAs ofthe present invention can use a coextrusion technique, such as thatdescribed in U.S. Pat. No. 5,660,922 (Herridge et al.). In a coextrusiontechnique, various molten streams are transported to an extrusion dieoutlet and joined together in proximity of the outlet. Extruders are ineffect the “pumps” for delivery of the molten streams to the extrusiondie. The precise extruder is generally not critical to the process. Anumber of useful extruders are known and include single and twin screwextruders, batch-off extruders, and the like. Conventional extruders arecommercially available from a variety of vendors such as from BerlynExtruders (Worcester, Mass.), Bonnot Manufacturing (Uniontown, Ohio),Killion Extruders (Cedar Grove, N.J.) and Leistritz Corp. (Sommerville,N.J.).

Other pumps may also be used to deliver the molten streams to theextrusion die. These include drum loaders, bulk melters, gear pumps, andthe like, and are commercially available from several sources such asGraco LTI (Monterey, Calif.), Nordson (Westlake, Calif.), IndustrialMachine Manufacturing Richmond, Va.), and Zenith Pumps Div., ParkerHannifin Corp. (Sanford, N.C.).

Typically, a feedblock combines the molten streams into a single flowchannel. The distinct layers of each material can be maintained with thelaminar flow characteristics of the streams. The molten structure thenpasses through an extrusion die, where the molten stream is reduced inheight and increased in width to provide a relatively thin and wideconstruction. This type of coextrusion is used to manufacture compositePSA forms having about 10 layers or more.

However, the use of a feedblock is optional, as a variety of coextrusiondie systems are known. For example, multimanifold dies may also beemployed, such as those commercially available from Cloeren Co. (Orange,Tex.) and EDI (Chippewa Falls, Wis.). In multimanifold dies, eachmaterial flows in its own manifold to the point of confluence. Incontrast, when feedblocks are used, the materials flow in contactthrough a single manifold after the point of confluence. Inmultimanifold die or feedblock manufacturing, separate streams ofmaterial in a flowable state are each split into a predetermined numberof smaller or sub-streams. These smaller streams are then combined in apredetermined pattern of layers to form an array of layers of thesematerials in a flowable state. The layers are in intimate contact withadjacent layers in the array. This array generally comprises a stack oflayers which is then compressed to reduce its height. In themultimanifold die approach, the adhesive width remains constant duringcompression of the stack, while the width is expanded in the feedblockapproach. In either case, a comparatively thin, wide adhesive filmresults. Layer multipliers in which the resulting adhesive film is splitinto a plurality of individual subfilms which are then stacked one uponanother to increase the number of layers in the ultimate adhesive filmmay also be used. The multimanifold die approach is typically used inmanufacturing composite PSA forms having less than about 10 layers.

In manufacturing the layered composite PSAs, the materials may be fedsuch that either the acrylic PSA or the polymer material forms theoutermost layers. When the polymer material is selected for theoutermost layers, it too, must be a PSA. The two outermost layers areoften formed from the same material, preferably the acrylic PSA. Thematerials comprising the various layers are preferably processable inthe same range of temperatures.

Significantly, although it has been generally believed that the meltviscosity of each of the various layers should be similar, i.e., theratio of their viscosities within a range of about 1:1 to about 2:1 atthe selected process temperature, this is not a necessary requirement ofthe methods and products of the present invention. However, concernswith encapsulation of one material within another where the layer ratiosare not uniform across the channel, suggest the viscosity ratio shouldgenerally not be greater than about 10:1. When the melt viscosities arenot closely matched, the material having the lowest melt viscosity waspreferred for the outer layers. Accordingly, residence times andprocessing temperatures may have to be adjusted independently (i.e., foreach type of material) depending on the characteristics of the materialsof each layer. For example, compare the extruder temperatures used inExamples 1-2, 3-10, and 11-12 in layered composite PSA forms each having13 layers.

The process stability, or the tendency of layers to break up, depends onthe volume fraction of the A and B layers, the viscosity ratios of thecomponent polymers or polymer mixtures, and the degree of shearthinning. For example, if the outer “A” layer has a higher viscositythan the “B” layer and has the same degree of viscosity shear thinning,process stability considerations suggest that the B layer have a greatervolume fraction than the A layer (i.e., above 50%). Conversely, if the Alayer has a lower viscosity than the B layer and has a greater degree ofshear thinning, process stability should increase if the B layer has asmaller (i.e., below 50%) volume fraction. These considerations aregenerally true regardless of the number of layers and the total flowrate of the process.

In melt processing polymeric multilayer composite PSAs, preferably, thedifference in elastic stresses generated at the interface between thelayers of different polymers are minimized to reduce or eliminate flowinstabilities that can lead to layer breakup. With knowledge of theelasticity of a material, as measured by the storage modulus on arotational rheometer over a range of frequencies (0.001 radians/s<ω<100radians/s) at the processing temperature, along with its viscosity atshear rates or frequencies less than 0.01 s⁻¹ (or a region in which theviscosity is constant with respect to shear rate or frequency) and thedegree to which the viscosity of the material shear thins, one of skillin the art can make judicious choices for the relative thickness of thelayers, the die gap, and the flow rate to obtain a film with continuous,uniform layers. Generally, the ratio of the viscosity to the storagemodulus at 0.01 s⁻¹ for the more viscous polymer should be greater thanthat of the less viscous polymer. Adding compatibilizer as required inthe present invention broadens the process window and contributes tomore stable and uniform layers.

Referring now to FIGS. 1(a) and 1(b), a cross-sectional magnified view(at 1000 and 1500×, respectively) of two layered adhesives, eachcontaining acrylic PSA layers and styrene-containing polymer layers, isshown. FIG. 1(a) shows one embodiment of the present invention, acomposite PSA that includes a compatibilizer. This compatibilizerincludes a styrene-compatible segment, and an acrylicadhesive-compatible segment. The inventive composite PSA exhibitsuniform layering and stability throughout the melt processing. Incontrast, FIG. 1(b), which includes no compatibilizer, shows unevenlayering and less stability.

Other manufacturing techniques, such as lamination, coating, orextrusion coating may be used in assembling layered composite PSAs andproducts from such layered composite PSAs according to the presentinvention. For example, in lamination, the various layers of theconstruction are brought together under temperatures and/or pressures(e.g., using temperature-controllable laminating rollers or a press)sufficient to adhere adjacent layers to each other.

In extrusion coating, a first layer is extruded onto a backing such as acast web, a uniaxially-oriented film, or a biaxially-oriented film, andsubsequent layers are sequentially coated onto the previously providedlayers. Extrusion coating may be preferred over the melt coextrusionprocess described above if it is desirable to pretreat selected layersof the multilayer film or if the materials are not readily processed bycoextrusion. Extrusion coating may be used to provide a barrier coatbetween the composite PSA of the present invention and a backingmaterial, such as an acrylic foam tape.

Continuous forming methods include drawing the composite PSA out of afilm die and subsequently contacting a moving plastic web or othersuitable backing. After forming, the composite PSA coatings are cooledand can be solidified more rapidly by quenching using either directmethods, such as chill rolls or water baths, or indirect methods, suchas air or gas impingement, or both.

Solvent casting may also be used to prepare the articles of the presentinvention. This method typically employs a common solvent, selected forcompatibility with the acrylic pressure-sensitive adhesive component,the polymer component, and the compatibilizer component. Such commonsolvents include, for example, toluene and tetrahydrofuiran. Specificselection of a common solvent for a particular subset of the presentinvention is within the skill of the art.

In the solvent casting method, the materials included in the compositePSA are blended to form a uniform mixture, then coated onto a carrierweb or a backing (described below) using a known coating technique suchas curtain coating, die coating, knife coating, roll coating, and spraycoating. A preferred coating method is knife coating. The solvent isthen dried away from the coated backing, usually with the aid of adrying oven for a time and temperature selected to remove anyundesirable level of residual solvent. The drying oven can activate athermal crosslinker as well. The composite PSA is then ready for furtherprocessing or use.

Backing materials useful with the present invention are preferablyflexible, and may be fabric, non-woven or woven polymeric films,metallic foils, paper, and/or combinations thereof. More specifically,film backings useful with the present invention include, for example,ethylene-propylene-diene rubbers, polyesters, polyisobutylenes,polyolefins, polyolefin-based nonwovens, polyurethanes, vinyls includingpolyvinylchloride and ethylene-vinyl acetate, and/or combinationsthereof. For particular purposes, the backing may be coated, one or bothmajor surfaces, with a primer or a release agent, which may be alow-adhesion backsize (LAB) material. For example, when using aplasticized polyvinylchioride (PVC) backing, an embodiment of thepresent invention comprising a butadiene- or isoprene-containing polymeralong with a polyisoprene-polyvinylpyridine (PI-PVP) compatibilizer hasa particular advantage in that the composite PSA has an affinity foracidic PVC.

Still other backings useful in the present invention includeacrylic-containing foam, polychloroprene-containing foam,polyolefin-containing foam, and polyurethane-containing foam, amongothers. Preferred foamed backings can be prepared as described in U.S.Pat. Nos. 4,223,067 and 4,415,615, which are herein incorporated byreference. In one such backing, glass microbubbles are uniformlydispersed into a polymerizable mixture. The mixture is then radiationpolymerized, with heat or ultraviolet energy. In another backing, apolymerizable composition is frothed, coated onto a backing, andpolymerized to achieve a cellular structure having at least 15% voids byvolume. Also, the backing can be foamed and polymerized without firstfrothing. Another preferred foam backing material is 5666 Acrylic FoamTape (available from Minnesota Mining and Manufacturing Company (3M),St. Paul, Minn.).

The composite PSAs of the present invention have improved mechanicalproperties, as compared to adhesive compositions that are similar excepthaving no compatibilizer. The stress-strain profiles of inventiveadhesive compositions and comparative adhesive compositions at twotemperatures are shown in FIGS. 2 and 3. These figures compare fivedifferent adhesives, of which two are embodiments of the presentinvention. Line 1 on the graph was an adhesive made from equal parts ofKraton™ 1107 and Escorez™ 1310; Line 2 was PSA A as described below;Line 3 was a 13-layer adhesive in an A(BA)₅BA form using the materialfrom Line 1 as the “B” layer and PSA A (Line 2) as the “A” layer,described below as Comparative Example 1; Line 4 was the same as Line 3,except the B layer included one wt % of apolyisoprene-poly-4-vinylpyridine (PI-PVP) compatibilizer, describedbelow as Example 1; and Line 5 was the same material as Line 3, exceptthat the B layer included one wt % of a polystyrene-poly-4-vinylpyridine(PS-PVP) compatibilizer.

In FIG. 2, the mechanical properties of these adhesives are compared at50° C. The strain in percent is plotted against the tensile stress inkilopascals (kPa). This graph shows that the composite PSAs of thepresent invention, which include compatibilizer (Lines 4 and 5), exhibitimproved tensile properties when compared to both the uncompatibilizedlayered adhesive (Line 3, Comparative Example 1) and even thehomopolymer PSAs (Lines 1 and 2). FIG. 3 shows these same compositionstested at 100° C., where one compatibilized (with PS-PVP) layeredadhesive (Line 5) demonstrated much better mechanical properties thanthe pure component PSAs, the uncompatibilized layered adhesive (Line 3),and the layered adhesive containing the PI-PVP compatibilizer (Line 4,Example 1), which has a lower Tg segment (polyisoprene rather thanpolystyrene).

Generally, adding compatibilizer in small amounts to at least onecomponent of a PSA having at least two components clearly improved theadhesive properties of the composite PSA thus formed, when compared to asimilar composition having no compatibilizer. These propertyimprovements become apparent during typical adhesive testing, such aspeel adhesion and static shear testing. The cohesive strength of acomposite PSA can be improved enough to shift the failure mode of a PSAtape, in shear and/or peel, from cohesive to adhesive. This means thatthe bond to a substrate is not weakened, while the composite PSA is muchstronger than a PSA having no compatibilizer, and the overall effect isbetter peel and shear properties.

The composite PSAs of the present invention also exhibit lesscoalescence upon aging than similar adhesives having no compatibilizer.The morphology of one composite PSA of the present invention is shown inFIG. 4(a). This composite PSA was exposed to 160° C. for one hour, afterwhich the image shown in FIG. 4(b) was taken. A comparison of theseimages leads to the conclusion that the inventive PSA morphology appearsstable. FIG. 5(a) shows the morphology of an adhesive similar incomposition to that shown in FIGS. 4(a) and (b), but having nocompatibilizer. FIG. 5(a) shows larger phase domains, as compared toFIG. 4(a). The FIG. 5(b) image is the same adhesive of FIG. 5(a) afterexposing the adhesive to 160° C. for one hour. The dramatic increase inthe size of the phase domains indicates much lower aging stability.

FIG. 6 compares cross-sectional digital images of scanning electronmicrographs taken at 500×magnification showing the morphology of anotheradhesive pair. In FIG. 6(a) a composite PSA of the present invention isshown. In FIG. 6(b) an adhesive similar in composition but withoutcompatibilizer is shown. The finer structure with smaller phase domainsin FIG. 6(a) indicates one advantage of this invention.

Therefore, this invention is useful in PSA articles having improved 180°peel adhesion, improved shear strength, improved interlayer adhesion,improved stability in coextruded layers, and reduced coalescence uponaging.

Objects and advantages of this invention are further illustrated by thefollowing examples, but the particular materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit this invention.

EXAMPLES

This invention is further illustrated by the following examples, whichare not intended to limit the scope of the invention. In the examples,all parts, ratios and percentages are by weight unless otherwiseindicated. The following test methods were used to characterize thepressure sensitive adhesive compositions in the examples.

Test Methods

180° Peel Adhesion Test

PSA composite samples having a size of 1.25 centimeters (cm) wide and 15cm long were tested for 180° peel adhesion to substrates of glass,smooth cast biaxially oriented polypropylene (PP) films, and/orstainless steel (SS) plates. The PSA samples were adhered to the testsubstrate surfaces using four passes of a 2.1-kilogram (kg) roller.After aging at controlled temperature and humidity conditions(approximately 22° C., 50% relative humidity) for approximately 24hours, the tapes were tested using a Model 3M90 slip/peel tester (fromImass, Inc., Accord, Mass.) in 180° geometry at 30.5 centimeter/minute(cm/min) peel rate, unless otherwise noted. Where noted, some sampleswere also aged at a controlled temperature of approximately 22° C. forapproximately 1 week and tested as above. The failure mode was noted asadhesive (A), cohesive (C), or mixed cohesive and adhesive (M).

Cold Temperature Peel Adhesion

The peel adhesion of the samples to a stainless steel substrate wasdetermined at various temperatures according to the ASTM StandardMethods of Testing Pressure-Sensitive Adhesive-Coated Tapes Used forElectrical Insulation, ASTM D1000-79, Procedure A. The peel rate used inthis test was 30.5 cm/min (12 in/min). The failure mode was noted asadhesive, cohesive, or mixed (cohesive and adhesive).

Room Temperature Shear Strength Test

Shear strength, as determined by holding time, was measured on PSAcomposite samples at controlled temperature and humidity conditions(approximately 22° C., 50% relative humidity). PSA samples having a sizeof 12.5 mm×12.5 mm were adhered to a stainless steel sheet with fourpasses of a 2.1-kg roller. A 1000-gram weight was hung from each sample.The amount of time for the weight to drop was recorded. If a sample didnot drop, the test was stopped after 10,000 minutes. The failure modewas noted as adhesive pop-off (P) if the sample detached from thesurface or cohesive (C) if the adhesive split.

Elevated Temperature Shear Strength Test

Shear strength, as determined by holding time, was also measured on PSAcomposite samples at specified elevated temperatures (e.g., 70° C.) andcontrolled humidity conditions (approximately 50% relative humidity).PSA samples having a size of 25.4 mm×25.4 mm were adhered tohigh-density polyethylene sheet with the pressure of four passes of a2.1-kg roller. The sample was allowed to dwell on the substrate for 20minutes before performing the test. Either a 750 or 500 gram weight washung from each sample. The amount of time for the weight to drop wasrecorded. The failure mode was noted as pop-off (P) or cohesive (C). Ifa sample did not drop, the test was stopped after 10,000 minutes.

Morphology

The morphology of the pressure-sensitive composites was analyzed usingoptical microscopy. Small samples (about 1 cm by 1 cm) were transferredfrom a release coated paper liner onto a glass microscope slide andcovered with a glass cover slip. The samples were imaged at amagnification of 250× using an Olympus BH2 optical microscope fittedwith a digital camera and an image analysis software package (all fromLECO Corp., St. Joseph, Mich.). The initial morphology was imaged andthe samples were subsequently annealed in a vacuum oven maintained at160° C. The morphology development was monitored over time, at thistemperature.

Alternatively, the morphology of composite PSA samples was determinedusing scanning electron microscopy (SEM). Sample cross-sections weremicrotomed using a diamond knife in a liquid nitrogen bath. Theresulting samples were treated with osmium tetraoxide vapors for 30minutes at ambient temperature (about 22° C.) to differentially stainthe isoprene component of the block copolymer phase of the blend. Thesamples were imaged at various magnifications using a JEOL model 820 SEM(available from JEOL Corp., Japan) operating at 10 kV. Stained phasesappeared white in these micrographs with the detector used(backscattering electron imaging).

Tensile Test

The tensile test was used to obtain stress-strain data for PSAcomposites. PSA samples having a width of 1.25 cm and a thickness of 500to 750 micrometers (μm) were made by repeatedly laminating PSA compositesamples having an initial thickness about 50 gm. The resulting sampleswere tested at various temperatures (25 to 150° C.) using a SintechModel 20 (available from MTS Systems Corp., Eden Prairie, Minn.)equipped with a temperature control chamber (ATS Series 2000 temperaturecontroller available from Applied Test Systems, Inc., Butler, Pa.). Theraw data was analyzed using TestWorks for Windows version 3.06 softwarepackage (from MTS Systems Corp.). A 4.5-kg (10-lb.) load cell was usedin these tests. All samples were tested at a crosshead speed of 50cm/min. Samples were tested along the machine direction.

Materials Used

PSA A: 95 parts isooctyl acrylate (IOA)/5 parts acrylic acid (AA), wateremulsion polymerized, shear viscosity—150 Pa-s, prepared according toU.S. Pat. No. RE 24,906, and dried.

PSA B: A suspension polymerized acrylic pressure sensitive adhesive wasprepared in accordance with U.S. Pat. No. 4,833,179 (Young et al.) asfollows. A 2-liter (L) split reactor equipped with condenser,thermowell, nitrogen inlet, stainless steel motor-driven agitator, and aheating mantle with temperature control was charged with 750 grams (g)deionized water, to which was added 2.5 g zinc oxide and 0.75 ghydrophilic silica (CAB-O-SIL EH-5, available from Cabot Corp.,Cambridge, Mass.) and was heated to 55° C. while purging with nitrogenuntil the zinc oxide and silica were thoroughly dispersed. At thispoint, a charge of 480 g isooctyl acrylate, 20 g methacrylic acid, 2.5 gazobisisobutyronitrile (AEBN) initiator (VAZO 64, available from DuPont,Wilmington, Del. (DuPont)) and 0.5 g isooctyl thioglycolate chaintransfer agent were mixed together. The resulting solution withinitiator and chain transfer agent was then added to the initial aqueousmixture while vigorous agitation (700 rpm) was maintained to obtain agood suspension. The reaction was continued with nitrogen purging for atleast 6 hours, during which time the reaction was monitored to maintaina reaction temperature of less than 70° C. The resulting pressuresensitive adhesive was collected and dried to at least 90% solids byweight.

PSA C: 90 parts IOA/10 parts AA, solution polymerized, inherentviscosity—0.7, prepared according to U.S. Pat. No. RE 24,906, and dried.

PSA D: 95 parts IOA/5 parts AA, solution polymerized, inherentviscosity—0.7, prepared according to U.S. Pat. No. RE 24,906, and dried.

PSA E: 93 parts IOA/7 parts AA, polymerized in a polyethylene shell asdescribed in U.S. Pat. No. 5,804,610 (Hamer et al.). This formulationalso contained 0.1 parts acryloyloxybenzophenone, a UV-activatedcrosslinking reagent.

PSA F: 57.5 parts IOA/35 parts methyl acrylatel 7.5 parts AA, solutionpolymerized, inherent viscosity—0.7, prepared according to U.S. Pat. No.RE 24,906, and dried.

Kraton™ D1107: A styrene-isoprene block copolymer commercially availablefrom Shell Chemical Co., Houston, Tex. (Shell).

Escorez™ 1310: A C5 aliphatic hydrocarbon tackifying resin commerciallyavailable from Exxon Chemical Co., Houston, Tex. (Exxon).

LDPE 1550P: Low density polyethylene commercially available from DowChemical Co. (Dow), Midland, Mich.

LLDPE 2517: Linear low density polyethylene available from Dow.

Styron™ 484: High impact polystyrene (HIPS), available from Dow.

Styron™ 615: Polystyrene (PS), available from Dow.

Styron™ 666D: Polystyrene (PS), available from Dow.

Bynel™ 50E561: Maleic anhydride grafted polypropylene, available fromDuPont.

Escorene™ 3445: Isotactic polypropylene, available from Exxon.

Solprene™ 411: A radial styrene-butadiene block copolymer having 30%styrene content, available from INSA, Houston, Tex.

Solprene™ 1205: A linear random-block styrene-butadiene copolymer having25% styrene content, available from INSA.

Piccolyte™ A135: An alpha-pinene resin tackifier available fromHercules, Inc., Wilmington, Del.

Shellflex™ 371: A naphthenic oil having 10% aromatics available fromShell.

Ethanox™ 330: A 1,3,5-trimethyl-2,4,6-tris (3,5-ditert-butyl-4-hydroxybenzyl) benzene antioxidant from Ethyl Corp.,Houston, Tex.

Compatibilizer A: Polyisoprene-block-4-vinylpyridine diblock copolymer(Degree of Polymerization, ((DP)PI=440, (DP)PVP=10) synthesized usinganionic polymerization techniques in a batch reactor. Isoprene,cyclohexane, and 4-vinylpyridine were purified by passage through acolumn of activated basic aluminum oxide (Brockmann I, available fromAldrich Chemical Co., Milwaukee, Wis.) and purged with argon and storedin a sealed flask at −20° C. until use. Isoprene (340 g, 5 mol) wascharged into a dry 5 L round bottomed flask fitted with septum andmagnetic stirbar. Cyclohexane (2 L) was subsequently charged into theflask. The resulting solution was purged vigorously with argon (researchgrade) for 10 min. A solution of sec-butyllithium (9.3 mL of a 1.3Msolution in cyclohexane) was charged into the flask. Tetrahydrofuran (10mL) was subsequently added to promote the reaction, and a light yellowcolor became apparent. The solution was stirred (with ice-water coolingbath to control the reaction exotherm) for 3 h. Then 4-vinylpyridine(17.1 g, 0.163 mol) was charged into the flask with vigorous stirring.The solution immediately became deep red in color. After 5 min.,isopropyl alcohol (10 mL) was added to quench the reaction. Theresulting polymer was poured into 15 L of isopropyl alcohol toprecipitate the polymer. The polymer was collected and dried undervacuum for 24 h to give a clear elastomer.

Compatibilizer B: PS-b-PVP synthesized using anionic polymerizationtechniques in a stirred tubular reactor previously described in U.S.Pat. No. 5,644,007. An initiator slurry was prepared by mixing 1884.64ml of 1.3M sec-butyl lithium solution in 4823.79 g of oxygen-freecyclohexane (Aldrich Chemical Co.) and stirred at room temperature forabout 30 minutes. Purified styrene monomer and purified toluene solventwere pressure fed or pumped (at rates of 136.11 g/min and 154.90 g/min,respectively) into the first zone of a 10 L stirred tube reactor(described in U.S. Pat. No. 5,644,007). The initiator slurry,continuously stirred under nitrogen to prevent stratification and oxygencontamination, was simultaneously introduced with the monomer andsolvent feeds at a rate of 19.64 ml/min using a peristaltic pump intothe first zone of the 10 L reactor. The overall solids loading of thisreaction was 44% in styrene monomer. A color change (orange-red) wasobserved in zone 1 when the initiator slurry contacted the monomer. Anexotherm in the first zone which was held at a constant temperature (65°C.) by adjusting the jacket temperature of zone 1 with ambienttemperature circulating water. The temperatures of zones 1 through 5 ofthe STR were individually maintained at 65, 40, 40, 40, and 20° C.,respectively. The living polymerization of styrene was allowed toproceed through the first 3 zones in a plug-like fashion, facilitated bystirring paddles along the reaction path over a period of approximately20 min, at which point all of the styrene monomer was consumed. At thestart of zone 4, purified 4-vinylpyridine was added (at a rate of 15.0g/min) resulting in another color change (to deep red) and was allowedto polymerize for approximately 7 minutes in this zone. Thepolymerization was subsequently quenched using either 2-propanol orhindered phenol thermal stabilizer (e.g., Irganox 1076 antioxidant, fromCiba-Geigy Corp. Greensboro, N.C.) in zone 5. The resulting viscoussolution was fed into a Discotherm B™ devolatilizer (from List AG,Acton, Mass.). The polymer solution was then devolatilized under vacuum(0.53-2.67 kPa; 4-20 torr) at 130° C., and hot-melt extruded. Theoverall residence time for these reactions was 30-35 minutes. Themolecular weight characteristics for this block copolymer weredetermined using gel permeation chromatography (GPC) analysis, with astyrene standard, and were as follows: Mn=28.8 kg/mol, polydispersityindex PDI)=1.69. The block copolymer composition was determined usingnuclear magnetic resonance (NMR) spectroscopy and was found to be: 88.9%PS: 11.1% PVP.

Compatibilizer C: Aliphatic amine-terminal polystyrene synthesized byusing anionic polymerization techniques as described in the literatureby Cemohous, et al., Macromolecules, 1998, 31, 3759-63. The resultingamine-terminal polystyrene samples molecular weight characteristics weredetermined to be as follows: Mn=19.7 kg/mol, PDI=1.10. It was also foundthat over 98% of this material had a single aliphatic amine at the chainend by both titration and ¹H NMR analysis.

Compatibilizer D: A random copolymer of 80 parts IOA, 5 parts AA, and 15parts styrene made in accordance with U.S. Pat. No. 5,753,768.

Compatibilizer E: A random macromer copolymer of 92 parts IOA, 4 partsAA, and 4 parts polystyrene macromer made in accordance with U.S. Pat.No. 4,693,776.

Compatibilizer F: Aminated polyethylene with 0.9 wt % amination was madeby melt mixing maleic anhydride-functionalized polyethylene (Fusabond™MB-226D, available from DuPont) with 3-dimethylaminopropyl amine (fromAldrich Chemical Co.) at 250° C. for approximately 10 minutes in acorotating twin screw extruder. A polymer filament output from theextruder die was directed into a water bath to quench the filament. Thenthe filament was passed over a roll of paper toweling to partially dryit, after which the polymer filament was pelletized.

Aziridine Crosslinker: 1,1-isophtaloyl-bis(2-methylaziridine) availablefrom Minnesota Mining and Manufacturing Company, St. Paul, Minn. (3M).

Macromelt™ 6240: A polyamide resin from Henkel, Inc., Elgin, Ill.

Examples 1-2, Comparative Example 1

Examples 1-2 illustrate the effect that the of addition of acompatibilizer had on the properties of pressure-sensitive adhesive(PSA) composite having an A(BA)₅BA multilayered construction.

In Example 1, a polymer, formed by melt-mixing 50 parts Kraton™ D1107and 50 parts Escorez™ 1310, and four parts compatibilizer,Compatibilizer A, were premixed into an “A” stream. The mixture ofpolymer and compatibilizer was fed by a corotating twin-screw extruder(34-mm Leistritz model LSM 34 GL, L/D of 42/1, available from LeistritzCorp., Sommerville, N.J.) operating with zone temperatures increasingfrom 150° C. to 204° C. into the “A” channels of a thirteen layerfeedblock (made as in U.S. Pat. No. 4,908,278). An acrylicpressure-sensitive adhesive, PSA A, was fed into a “B” stream by asingle screw extruder (50-mm Bonnot Model 2WPKR, from BonnotManufacturing, Uniontown, Ohio), operating with zone temperaturesincreasing from 162° C. to 177° C. into the inner six “B” channels ofthe feedblock. The “A” and “B” streams were merged in the feedblock intoa multilayered flow stream that was passed through a single 25 cm (10inch) wide orifice film die (from Extrusion Dies, Inc. (EDI), ChippewaFalls, Wis.) and drop cast onto a 51 μm thick polyethyleneterephthalate(PET) film. This yielded 78 parts PSA A (I), 22 parts polymer (II) and 1part Compatibilizer A (III) in the overall composition. A release linerwas applied to the exposed surface of the cast adhesive layer, and thecombination was passed over a chill roll to form a multilayer PSAcomposite sandwiched between a single layer PET film and a releaseliner. The temperatures of the feedblock, die and chill roll were set at154, 150 and 18° C., respectively, and the line speed was about 8.4meters per minute (m/min.). The PSA composite had an overall measuredthickness of 150 μm and a calculated material weight ratio of PSA A topolymer to compatibilizer of 78:22:1.

Example 2 was made as in Example 1 except that the amount ofCompatibilizer A was increased to give 3 parts Compatibilizer A per 100parts of the total composition. The line speed for Example 2 was reducedto 4.6 m/min. to result in a composite PSA having a thickness of about425 μm.

Comparative Example 1 was made substantially as in Example 1 except thatno compatibilizer was used.

All examples were tested for 180° peel adhesion (with a surface ofeither glass or polypropylene (PP)) and room temperature shear strength.All shear strength samples failed cohesively. The results are shown inTable 1, where the material ratio is PSA A (I), polymer (II), andCompatibilizer A (III).

TABLE 1 Material Peel RT Ratio Thickness Peel Failure Shear Ex. I:II:IIISurface (μm) (N/dm) Mode (min.) 1 78:22:1 Glass 147 83.1 C 165 2 78:22:3Glass 425 148.2 C 75 CE 1 78:22:0 Glass 150 34.1 C 19.6 1 78:22:1 PP 14781.1 A — 2 78:22:3 PP 425 145.9 A — CE 1 78:22:0 PP 150 46.7 C —

The data in Table 1 indicates that peel adhesion more than doubled whenas little as 1 wt % of compatibilizer was used. In addition, the shearstrength increased over 8 times when as little as 1 wt % compatibilizerwas included in the composite PSA.

Examples 3-10, Comparative Examples 2-3

Examples 3-10 illustrate the effect of the type of compatibilizer andthe use of electron beam curing on the properties of another PSAcomposite having 13 layers in the form of A(BA)₅BA.

Examples 3-6 were made in a manner similar to Example 1 except that PSAB was used in place of PSA A, different types and amounts ofcompatibilizers were used, and some process conditions were changed. Thematerial ratio used was 78 parts PSA B to 22 parts polymer. Thecompatibilizer type and amount per 100 parts of the total compositionare shown in Table 2. The line speed was varied to achieve a total PSAcomposite thickness as reported in Table 2. The temperatures of thefeedblock and the die were set at 154° C. and 149° C., respectively.

Comparative Example 2 was made in a manner similar to Example 1 exceptno compatibilizer was used and the line speed was varied to achieve athickness similar to Examples 3-6. The overall thickness was varied bychanging the line speed from 3.7 m/min for Examples 3, 4, 5 and 6 to 7.6m/min. for Comparative Example 3.

Examples 7-10 and Comparative Example 3 were as Examples 3-6 andComparative Example 2 except that they were irradiated with an electronbeam, exposing each composite to 50 kiloGray (kGy) at 175 kiloVolts(kV).

Examples 3-10 and Comparative Examples 2 and 3 were tested for 180° peeladhesion to glass and the failure mode was noted. The results are shownin Table 2.

TABLE 2 Compatibilizer Thickness Peel to glass Failure Ex. Type Parts μmN/dm Mode 3 B 0.5 58 20.6 C 4 C 0.5 62.5 18.4 M 5 D 5.0 80 16.9 M 6 E5.0 80 12.0 A CE 2 none — 87.5 19.3 C 7 B 0.5 58 25.0 A 8 C 0.5 62.529.8 A 9 D 5.0 80 18.3 A 10 E 5.0 80 23.9 A CE 3 none — 87.5 22.4 C

As shown in Table 2, the type and amount of compatibilizer can have adramatic effect on the adhesive properties. Adding Compatibilizer C andD to PSA B, in Examples 4 and 5, changed the failure mode from cohesiveto mixed, relative to Comparative Example 2. Adding 5% of CompatibilizerE to PSA B changed the failure mode to adhesive. The differences in peelwere significantly impacted by the peel mode, with the peel ofComparative Example 2 being a measurement of adhesive splitting.

As shown by Examples 7-10, relative to Examples 3-6, electron beamcuring dramatically increased the interlayer and peel adhesion in thesecomposite PSAs. The uncompatibilized Comparative Example 3 was impactedlittle by electron beam curing and still suffered from cohesive failureduring the peel test. Each of the compatibilized examples had increasedpeel adhesion values after curing. For example, Compatibilizer C presentat only 0.5 wt % (Examples 4 and 8) increased peel adhesion from 18.4N/dm to 29.8 after electron beam curing. In addition, the failure modesof each composite PSA after electron beam curing was adhesive, ratherthan cohesive or mixed.

While the peel adhesion of Example 9 was not higher than that ofComparative Example 3, there was an improvement in that the failure modechanged from cohesive to the preferred failure mode, adhesive.

The addition of compatibilizer also promoted the generation of moreuniform layers in this microlayer form of composite PSA. FIGS. 3(a) and3(b) are scanning electron micrographs for cross-sections ofcompatibilized Example 3 and uncompatibilized Comparative Example 2. Thelayered structure in Example 3 appears more uniform than that inComparative Example 2.

Examples 11-12, Comparative Examples 4-5

Examples 11-12 illustrate the effect of material weight ratio on theproperties of a PSA composite having an A(BA)₅BA multi-layer form.

Examples 11-12 were made substantially as Example 1 except the polymerwas Styron™ 484 HIPS, the compatibilizer was Compatibilizer B, thecalculated material ratios were different, the polymer was fed into the“B” channels of the feedblock, the acrylic PSA into the “A” channels,and process conditions were changed. The calculated material ratios ofthe PSA, the polymer and the compatibilizer for Examples 11 and 12 were90:10:1 and 93:7:1, respectively. The temperature of the feedblock anddie for each example was increased to 204° C. and the line speed wasdecreased to 3.7 m/min to result in a total composite thickness for eachexample as reported in Table 3.

Comparative Examples 4 and 5 were made as in Examples 11 and 12,respectively, except that each contained no compatibilizer.

Examples 11-12 and Comparative Example 4-5 were tested for 180° peeladhesion to glass and RT shear strength. The results are shown in Table3.

TABLE 3 Peel to Peel RT Shear Material Thickness glass Failure ShearFailure Ex. Ratio (μm) (N/dm) Mode (min.) Mode 11 90:10:1 50 17.6 A 39.6C CE 4 90:10:0 63 6.3 A 7.5 C 12 93:7:1 75 28.0 A 25.7 C CE 5 93:7:0 759.7 A 5.4 C

The data in Table 3 shows that peel adhesion increased around 300% when1% of Compatibilizer B was added into the PSA composite, and the shearstrength increased.

Example 13 and Comparative Example 6

Example 13 illustrates the effect of different compatibilizers on PSAproperties in a composite having 13 layers in an A(BA)₅BA form.

Example 13 was made as in Example 1 except that the polymer andcompatibilizer were different, the material weight ratio was changed,the polymer was fed into the “B” channels of the feedblock, the acrylicPSA into the “A” channels, and some process conditions were altered. Thepolymer was LLDPE and the compatibilizer was Compatibilizer F. Thematerial weight ratio of PSA A, polymer, and Compatibilizer F was97:3:3. The line speed was 3.7 m/min.

Comparative Example 6 was made as Example 13 except that nocompatibilizer was present, the material weight ratio of PSA to polymerwas 97:3 and the line speed was increased to 5.2 m/min to achieve athickness similar to Example 13.

These examples were tested for peel 180° peel adhesion to glass and roomtemperature shear strength. The data is shown in Table 4.

TABLE 4 Material Thickness Peel to glass Failure Example Ratio (μm)(N/dm) Mode 13 97:3:3 92.5 42.2 A CE 6 97:3:0 92.5 11.9 C

The data illustrated the pronounced effect of adding compatibilizer tothe composite. Peel adhesion was increased more than 275% and thefailure mode switched from cohesive to adhesive when a compatibilizerwas added to the composite.

Examples 14-15 and Comparative Example 7-8

Examples 14-15 illustrate the effects of compatibilizer in PSAcomposites having 25 layers of an ACBC(ACBC)₅A form, where A, B, and Care layers of different polymers, of which at least A is a PSA.

In Example 14, an adhesive, PSA B, was fed by a single screw extruder(Bonnot Model 2WPKR), operating with zone temperatures increasing from177 to 188° C. into the “A” channels of a 25 layer feedblock. A polymercomposed of a dry-blend mixture of 38 parts Styron™ 484 HIPS and 50parts Stryon™ 615 PS, was fed in a ratio of 88 parts of the polymermixture and 12 parts of a compatibilizer, Compatibilizer B, with asingle screw extruder equipped with gear pump (19 mm Killion KLB-075,L/D=32, from Killion Extruders, Cedar Grove, N.J.), operating with zonetemperatures increasing from 160 to 232° C., into the “B” channels ofthe feedblock. Another material, a mixture of 80 parts Kraton™ D1107 and20 parts Escorez™ 1310 was fed with a single screw extruder with a gearpump at the extruder discharge (51 mm, Berlyn 2 Extruder, L/D of 32/1,available from Berlyn Extruders, Worcester, Mass.) operating with zonetemperatures increasing from 49 to 177° C., into the “C” channels of thefeedblock. The streams were merged in the feedblock into a multi-layeredflow stream that was passed through a single orifice film die 46 cm (18inches) wide (from EDI). The flow stream was drop cast between tworelease liners as they passed over a chill roll, contacting one releaseliner, to produce a multilayer form. The temperatures of the feedblock,die and chill roll were set at 188, 188 and 52° C., respectively, andthe line speed was 4.3 m/min. The multilayer film had an overallmeasured thickness of approximately 85 μm. The calculated material ratioof PSA B in the A layer, to material in the B layer, to polymer in the Clayer was 66:8:26. Within layer B, the ratio of polymer tocompatibilizer was 88:12. Thus, the overall ratio of combined polymerand adhesive to compatibilizer was 99:1.

Example 15 was made as Example 14 except conditions were adjusted toachieve a calculated material ratio of layer A: layer B: layer C of48:5:47. Within layer B, the ratio of polymer to compatibilizer was88:12. The overall ratio of combined polymer and adhesive tocompatibilizer was therefore 99.4:0.6.

Comparative Examples 7 and 8 were made as Examples 15 and 16,respectively, except that the polymer mixture was one part HIPS to onepart PS and no compatibilizer was present.

Examples 14-15 and Comparative Examples 7-8 were tested for 180° peeladhesion to glass and room temperature shear strength. These adhesivesranged from 80 to 85 μm in thickness. The results are shown in Table 5.

TABLE 5 Material Polymer in Peel to Failure Ratio Layer B to Glass Peelto PP Mode Ex. A:B:C Compatibilizer (N/dm) (N/dm) (glass/PP) 14 68:8:24 88:12 20.7 20.9 A/A CE 7 68:8:24 100:0 11.9 14.7 A/A 15 48:5:47  88:1231.9 30.1 A/A CE 8 48:5:47 100:0 27.3 29.2 C/C

As seen, a multi-layered composite PSA that included another material(having compatibilizer) located between alternating regions of PSAexhibited as much as a 74% increase in peel adhesion relative to theComparative Examples that did not contain compatibilizer. Moreinterestingly, only adhesive failure modes were witnessed during thepeel test for Examples 14 and 15 while the uncompatibilized ComparativeExample 8 failed cohesively to both PP and glass surfaces.

Examples 16-21 and Comparative Examples 9-11

Examples 16-21 illustrated the effect that a compatibilizer had on theadhesive properties of blended composite PSAs.

In Example 16, 30 parts of a polymer, composed of one part Kraton™ D1107and one part of an additive, tackifier Escorez™ 1310, was dissolved in70 parts of a solvent, (toluene) to form a solution. To this solutionwas added 3 parts of a compatibillzer, Compatibilizer A. The solutionwas stirred for 10 minutes at 21° C. In a separate solution, 30 parts ofan adhesive, PSA C was dissolved into 70 parts toluene over a period of24 h. Then 30 parts of the Kraton™ D1107 solution was subsequently mixedwith 70 parts of the PSA C solution for 24 hours at 21° C.

The resulting solution was applied with a knife coater onto one side of35-μm thick PET substrate and placed for 10 minutes in an oven set at70° C. to remove the solvent. The composite PSA on the substrate had athickness of about 50 μm and a material ratio of PSA C, polymer andcompatibilizer of 70:30:1.

Examples 17-21 were made as Example 16 except that the amounts of PSA C(A), polymer (B), and Compatibilizer A (C) were varied as reported inTable 6.

Comparative Examples 9-11 were made as Examples 16, 18 and 20,respectively except that no compatibilizer was included.

The examples were tested for 180° peel adhesion to glass at both 0.3 and2.3 m/min peel rate (12 and 90 inch/min), and room temperature (RT)shear strength. The test results are shown in Table 6. All RT shearsamples failed cohesively.

TABLE 6 Material Ratio Peel (N/dm) RT Shear Ex. A:B:C 0.3 m/min 2.3m/min (min) 16 70:30:1 61.4 80.5 83 17 70:30:2 61.6 81.4 101 CE 970:30:0 59.0 90.9 61 18 50:50:1 61.8 86.7 128 19 50:50:2 63.6 88.7 147CE 10 50:50:0 58.7 91.5 402 20 30:70:1 67.1 99.9 1,152 21 30:70:2 64.293.5 1,680 CE 11 30:70:0 56.5 85.1 2,152

These results showed that the peel adhesion and shear strength dependupon the composition of these solvent-borne PSAs, while the level ofcompatibilizer had only a small impact. The samples with 30 wt % A and70 wt % B (examples 20 and 21, relative to Comparative Example 11)showed improvement in peel but reductions in shear strength whencompatibilizer was used. The samples with 70 wt % A and 30 wt % B(Examples 16 and 17, relative to Comparative Example 9) had similar orlower peel adhesion and higher shear when compatibilizer was used. Thesamples with equal parts A and B (Examples 18 and 19, relative toComparative Example 10) showed improvement in peel adhesion at the lowrate, but reductions in peel adhesion at the high rate and reductions inshear strength when compatibilizer was used.

Examples 22-23 and Comparative Example 12

Examples 22-23 illustrate the effect that heat aging had on theresulting morphology and adhesive properties in blended composite PSAs.

Examples 22-23 were made as described in Example 16 except that theamounts of compatibilzer were as shown in Table 7 (below) and sampleswere subsequently exposed to various aging conditions. The resultingtapes were vacuum heat-aged at a pressure of 0.67 to 2.67 kPa (5 to 20torr) and a temperature of 160° C. for either one or three hours.

Comparative Example 12 was made as Example 22 except no compatibilizerwas present.

The examples were tested for 180° peel adhesion to glass at and roomtemperature shear strength. The test results are shown in Table 7, wherethe material ratio is PSA C (A), polymer (B), and Compatibilizer A (C).

TABLE 7 Aging Peel from Material Ratio Time Glass Failure Ex. A:B:C (h)(N/dm) Mode 22A 70:30:0.25 1 104.5 A 23A 70:30:2 1 112.9 A CE 12A70:30:0 1 121.4 A 22B 70:30:0.25 3 105.4 A 23B 70:30:2 3 113.0 A CE 12B70:30:0 3 134.0 C

Comparing the peel adhesion (at 0.3 m/min) of Example 17 in Table 6 withExamples 23A and 23B in Table 7 showed that the peel adhesion of tapesmade with composite PSAs that contained some compatibilizer did notbuild as rapidly with heat aging as that of tapes that did not containcompatibilizer (Comparative Examples 9, 12A, and 12B). Moresignificantly, the composite adhesive retains the desirable adhesivefailure mode, even after the adhesion to glass increases, an effectknown to occur with acrylic adhesives.

FIGS. 4(a) and 4(b) show the morphology of Example 23A before and after(Ex. 23B) heat aging under vacuum 0.67 to 2.67 kPa (5-20 torr) at 160°C. for one hour. FIGS. 5(a) and 5(b) show the morphology of ComparativeExample 12A before and after (CE 12B) similar aging conditions. Thesefigures clearly show that the morphology is more uniform in samples thatcontain compatibilizer, as compared to samples having no compatibilizer.These micrographs also demonstrated that the compatibilized blendmorphology did not coarsen (i.e., the size of the phase domains did notincrease) with heat aging while the uncompatibilized blend considerablycoarsened. This coarsened blend also showed the undesirable shift to thecohesive failure mode, while the composite adhesive of the presentinvention retained the preferred adhesive failure mode even afterextended heat aging.

Examples 24-25 and Comparative Example 13

Examples 24-25 illustrate the effect that a compatibilizer had on PSAproperties at below-ambient temperatures in composite PSAs in formscomposed of mixtures of PSA regions and polymer regions.

Examples 24-25 were made as Example 16-17, respectively except PSA D wasused instead of PSA C, and the composite adhesive solutions were coatedonto a release liner, dried and subsequently laminated to an stretchablebacking made of plasticized polyvinylchloride (PVC) (from 3M) that wasflexible at −18° C.

Comparative Example 13 was made as Example 24 except no compatibilizerwas included.

The examples were tested for cold temperature peel adhesion at varioustemperatures. The test results are shown in Table 8, where the materialratio is PSA D (A), polymer (B), and Compatibilizer A (C).

TABLE 8 Material Ratio Temperature Peel Example A:B:C (° C.) (N/dm) 24A70:30:1 25 63.8 25A 70:30:2 25 65.8 CE 13A 70:30:0 25 55.9 24B 70:30:1−10 153.1 25B 70:30:2 −10 156.6 CE 13B 70:30:0 −10 117.9 24C 70:30:1 −18158.4 25C 70:30:2 −18 169.0 CE 13C 70:30:0 −18 135.5

The data in Table 8 showed that the addition of compatibilizer had apronounced effect on peel adhesion performance at low temperatures whena stretchable backing was used. At room temperature, the peel adhesionvalues of compatibilized blends was as much as 17% greater than thecontrol. The inventive composite PSA samples were clearly superior tothe comparative examples when tested at lower temperatures.

Example 26 and Comparative Example 14

Example 26 demonstrates the effect of a compatibilizer on composite PSAproperties in the form of mixtures made using hot melt compounding andcoating techniques.

In Example 26, 35 parts of a polymer, composed of one part Kraton™ D1107and one part of an additive, tackifier Escorez™ 1310, was mixed with onepart of a compatibilizer, Compatibilizer A, in a 300 cm³ bowl Brabenderbatch mixer (from Brabender Instruments, South Hackensack, N.J.)operating at 50 rpm and 160° C. for 10 min. An adhesive, PSA A, wasintroduced to the mixture after 5 minutes and the total mixture was thenprocessed for 5 minutes to form a composite PSA The composite PSA wassubsequently fed by a Bonnot extruder (Donnot Model 2WPKR, 50 mm fromBonnot Manufacturing, Uniontown, Ohio) into a twin-screw extruder (18 mmHaake Micro18 Extruder, available from Leistritz, Corp.). Thetemperature was maintained at 177° C. (350° F.) in each of the six zonesof the twin-screw extruder, which was continuously discharged at apressure of at least about 0.69 MPa (100 psi) into a 15.2-cm (6-inch)wide rotary rod die. The die was maintained at 177° C. (350° F.) and thedie gap was 0.5 to 0.8 mm (20 to 30 mils). The adhesive composite wascoated onto a 51-μm (2-mil) thick biaxially oriented PET film and arelease coated paper web was laminated onto the adhesive, all at a rateof 1.36 kg/h (3 lb/h). The construction was fed at a rate of 4.6 m/min(15 fpm) between chill rolls maintained at a temperature of 21° C. (70°F.) to form an adhesive tape with a composite PSA layer thickness ofabout 50 μm (2.0 mils). Alternatively, some blended composite PSA wasfed between two release-coated paper webs for further testing of thecomposite PSA layer or subsequent transfer of the composite PSA layer toa different substrate.

Comparative Example 14 was made as Example 26 except no compatibilizerwas added.

The examples were tested for 180° peel adhesion to glass in the down-weband cross-web directions and RT shear. The test results are shown inTable 9, where the material ratio is PSA A (A), polymer (B), andCompatibilizer A (C).

TABLE 9 Shear Material Ratio Down-Web Peel Cross-Web Peel Strength Ex.A:B:C (N/dm) (N/dm) (min) 26 65:35:1 84.5 55.2 6.5 CE 14 65:35:0 55.846.0 2.3

The Table 9 data showed that the peel adhesion values observed for theblended composite PSA was as much as 52% higher than theuncompatibilized blend. In addition, the anisotropic peel adhesioncharacteristic was more pronounced in the inventive composite PSA,showing a difference of 53 percent versus only 21 percent for theuncompatibilized comparative example. Scanning Electron Micrographs(SEM) of these two different systems are shown in FIGS. 6(a) and 6(b).These micrographs show that the domains for the compatibilized blendwere more oriented and continuous in nature as compared to theuncompatibilized blend.

Examples 27-34 and Comparative Examples 15-18

Example 27-34 demonstrate the effect of a compatibilizer on the adhesiveproperties of composite PSAs in the form of mixtures that were madeusing a solventless process.

In Example 27 a polymer, Styron™ 666D PS, was fed into the feed throatof a twin-screw extruder (30-mm diameter, fully-intermeshing,co-rotating extruder, L/D 37/1, available from Werner Pfleiderer Co.,Ramsey, N.J.). A compatibilizer, Compatibilizer B, was fed into zone 3of the extruder, and an adhesive, PSA E, was introduced into zone 5, toform a melt mixture having a material ratio of PSA E to polymer toCompatibilizer B of 97:2.5:0.5. The temperatures used in zones 1-6 were149, 204, 204, 191, 191, and 191° C., respectively. The melt mixture waspassed through a 25.4-cm (10-inch) wide film die (Ultraflex™ 40 die,Model 89-12939, from EDI). The die was maintained at 204° C. (400° F.)and the die gap was 0.5 to 0.8 mm (20 to 30 mils). The melt mixture wasapplied to a 51-μm (2-mil) differential release-coated paper liner underconditions resulting in a composite PSA thickness of about 51 μm (2mil). The liner and composite PSA were fed at a rate of 6.4 m/min (20fpm) between chill rolls maintained at a temperature of 21° C. (70° F.).

Example 28 was made as Example 27 except the composite PSA was furtherirradiated online with a dose of 500 mJ/cm² of TV radiation (highintensity UV B light source, model 14498 from UVEX Inc., Smithfield,R.I.).

Example pairs 29 & 30, 31 & 32 and 33 & 34 were made as Examples 27 &28, with the second sample of each pair having UV exposure, except thatthe material (weight) ratios were 97:1:2, 85:14.5:0.5, and 85:13:2,respectively.

Comparative Examples 15-18 were made as Examples 25, 29, 31 and 33,respectively, except compatibilizer was replaced with polymer.

The examples were tested for 180° peel adhesion to glass and RT shearstrength. The test results are shown in Table 10, where the materialratio is PSA E (A), polymer (B), and Compatibilizer B (C).

TABLE 10 Material Shear Ratio UV Dose Peel Shear Failure Ex. A:B:C(mJ/cm²) (N/dm) (min) Mode 27 97:2.5:0.5 0 46.6 1.6 C 28 97:2.5:0.5 50044.0 3980 P 29 97:1:2 0 49.3 3.7 C 30 97:1:2 500 40.9 7950 P CE 1597:3:0 0 47.7 1.4 C CE 16 97:3:0 500 42.0 660 C 31 85:14.5:0.5 0 31.72.4 P 32 85:14.5:0.5 500 28.9 10,000 none 33 85:13:2 0 33.9 4.1 C 3485:13:2 500 32.4 7405 P CE 17 85:15:0 0 44.7 2.1 C CE 18 85:15:0 50037.0 645 C

As seen in Table 10, adding compatibilizer to these mixture systemsimproved the shear strength of the resulting tapes as much 1500% whenthe adhesives were irradiated. In addition, the compatibilized systemsthat were UV-cured either did not fail the shear test or failedadhesively (pop-off), whereas the UV-irradiated uncompatibilized tapesall still failed cohesively.

Examples 35-36 and Comparative Example 19

Examples 35-36 demonstrate the effect of a chemical crosslinker on theadhesive properties of a composite PSA in the form of a mixture.

In Example 35, a polymer solution was made by dissolving 13.2 partsSolprene™ 411, 7.1 parts Solprene™ 1205, 20.3 parts Piccolyte™ A135, 2.0parts Shellflex™ 371, and 0.4 parts Ethanox™ 330 in toluene to form asolution having 43% solids. A compatibilizer, Compatibilizer B, wasadded to this solution in the amount of 0.34 parts compatibilizer to 100parts total solution, and the mixture was blended at room temperaturefor 15 to 30 minutes. Another solution was made by mixing an adhesive,PSA F, into a solvent mixture of 29 parts toluene and 71 parts ethylacetate to form a solution having 25% solids.

A chemical crosslinker, 1,1-isophtaloyl-bis(2-methylaziridine) (from3M), was added to this adhesive solution in the amount of 0.02 partscrosslinker to 100 parts total solution and mixed at room temperaturefor 15 to 30 minutes.

The two solutions were combined and mixed at room temperature for 30minutes to form a composite PSA solution of 34 percent solids. Thiscomposite PSA solution was applied with a coating die onto a releaseliner moving at about 18.3 m/min (60 fpm), dried and crosslinked in anoven having a temperature profile of 50, 60, 70, 76° C. The compositePSA on the release liner, after drying away the solvents, had athickness of about 50 μm and a material ratio of PSA F, polymer andCompatibilizer B of 36:64:0.5.

A barrier coat, Macromelt 6240, was extrusion-coated to a targetthickness of about 25 μm (0.5 mils) onto the adhesive surface of thecomposite PSA immediately after the web left the last oven zone. Thebarrier-coated side of the construction was subsequently laminated usinga hand roller at room temperature (21° C.) to an acrylic foam tapebacking (No. 5666, available from 3M) to form a foamed-backed compositePSA tape. This tape was allowed to stand for at least 24 hours beforetesting.

Example 36 was made as Example 35 except that the material ratio of PSAF to polymer to Compatibilizer B was 36:64:1.

Comparative Example 19 was made as Example 35 except that nocompatibilizer was added.

The examples were tested for elevated-temperature shear performance, 90°peel adhesion, and for peel adhesion and shear strength with a highdensity polyethylene substrate. The results are shown in Tables 11 and12, where the material ratios were PSA F (A), polymer (B), andCompatibilizer B (C).

TABLE 11 Material Ratio Mass of 70° C. Shear Failure Example A:B:C Load(min) Mode 35A 36:64:0.5 500 g 10,000 none 36A 36:64:1.0 500 g 10,000none CE 19A 36:64:0 500 g 900 C 35B 36:64:0.5 750 g 10,000 none 36B36:64:1.0 750 g 3,500 P CE 19B 36:64:0 750 g 40 C

As seen in the above table, the shear strength was significantlyimproved with a 500 g load and more a 750 g load, relative to theuncompatiblized blend examples when only 0.5% of compatibilizer wasadded to the mixture form of the composite PSA. Performance improvementsalso were witnessed with higher compatibilizer loading.

TABLE 12 Example Material Ratio (A:B:C) Peel (N/dm) Failure Mode 3636:64:1 271 Foam split CE 19C 36:64:0 253 A

As seen in Table 12, foam tape assemblies having either the compositePSA or uncompatiblized blend gave acceptable peel adhesion values. Thefailure mode of these tapes was adhesive in the case of the comparativeexample, however, in the compatibilized example split the acrylic foamcore during peel, a desirable result.

These examples show that the composite PSA in these embodiments of theinvention have dramatically improved shear strength, as compared to asimilar adhesive having no compatibilizer, while not compromising peeladhesion.

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scopeand principles of this invention, and it should be understood that thisinvention is not to be unduly limited to the illustrative embodimentsset forth hereinabove.

We claim:
 1. A composite pressure-sensitive adhesive comprising: fromabout 95 to about 5 parts by weight of an acrylic pressure-sensitiveadhesive; from about 5 to about 95 parts by weight of an at leastpartially soluble styrene-containing polymer; and a compatibilizerpresent in the composite pressure-sensitive adhesive in an amountgreater than 0 to about 10 parts by weight of the compositepressure-sensitive adhesive, the compatibilizer having a structureselected from the group consisting of (1) an acrylic adhesive-compatiblesegment and a polymer-compatible segment wherein at least a portion ofthe compatibilizer is present substantially throughout either theacrylic adhesive, the polymer, or both, and (2) an acrylicadhesive-reactive segment and a polymer-compatible segment wherein atleast a portion of the compatibilizer is present substantiallythroughout the polymer.
 2. The composite pressure-sensitive adhesive ofclaim 1 wherein the acrylic adhesive and the polymer are arranged inalternating layers.
 3. The composite pressure-sensitive adhesive ofclaim 2 comprising from 5 to 100 layers.
 4. The compositepressure-sensitive adhesive of claim 3 having an overall thickness belowabout 250 μm.
 5. The composite pressure-sensitive adhesive of claim 1further comprising crosslinks.
 6. The composite pressure-sensitiveadhesive of claim 1 having at least one pressure-sensitive adhesiveproperty from the group consisting of a room temperature shear strengthgreater than about 10,000 minutes, a peel adhesion greater than that ofa substantially similar composite pressure-sensitive adhesive having nocompatibilizer, and a 500-gram weight 70° C. shear strength greater thanthat of a substantially similar composite pressure-sensitive adhesivehaving no compatibilizer.
 7. The composite pressure-sensitive adhesiveof claim 1 wherein the acrylic adhesive and the polymer are in a mixturein which the adhesive is in a phase that is continuous and the polymeris in a phase that is discontinuous or co-continuous.
 8. Apressure-sensitive adhesive article comprising a backing having opposingsurfaces, at least one of the surfaces bearing thereon the compositepressure-sensitive adhesive of claim
 1. 9. The pressure-sensitiveadhesive article of claim 8 wherein the backing is selected from thegroup consisting of non-woven fabrics, woven fabrics, paper, metallicfoils, polyester films, polyisobutylene films, polyolefin films,polyolefin-based nonwovens, polyurethanes, vinyl films, and combinationsthereof.
 10. The pressure-sensitive adhesive article of claim 8 whereinthe backing is selected from the group consisting of anacrylic-containing foam, polychloroprene-containing foam,polyolefin-containing foam, and polyurethane-containing foam.
 11. Thepressure-sensitive adhesive article of claim 8 wherein the backingcomprises a blend of ethylene-vinyl acetate and ethylene-propylene-dienerubber.
 12. The composite pressure-sensitive adhesive of claim 1 whereinthe polymer component is a pressure-sensitive adhesive.
 13. A compositepressure-sensitive adhesive comprising: from about 95 to about 5 partsby weight of an acrylic pressure-sensitive adhesive; from about 5 toabout 95 parts by weight of a styrene-containing polymer; and acompatibilizer, which is not a reaction product of the acrylicpressure-sensitive adhesive and the polymer, present in the compositepressure-sensitive adhesive in an amount greater than 0 to about 10parts by weight of the composite pressure-sensitive adhesive, thecompatibilizer having a structure selected from the group consisting of(1) an acrylic adhesive-compatible segment and a polymer-compatiblesegment wherein at least a portion of the compatibilizer is presentsubstantially throughout either the acrylic adhesive, the polymer, orboth, and (2) an acrylic adhesive-reactive segment and a segment whereinat least a portion of the compatibilizer is present substantiallythroughout the polymer.
 14. A composite pressure-sensitive adhesivecomprising: from about 95 to about 5 parts by weight of an acrylicpressure-sensitive adhesive; from about 5 to about 95 parts by weight ofan at least partially soluble styrene-containing polymer; and acompatibilizer present in the composite pressure-sensitive adhesive inan amount greater than 0 to about 10 parts by weight of the compositepressure-sensitive adhesive, the compatibilizer having the formula R⁴-Y,wherein: R⁴ is a styrene-containing segment and Y is a segment selectedfrom the group consisting of: a) at least one alkyl acrylate ester,wherein the alkyl group contains from 1 to about 20 carbon atoms, and b)at least one functional group capable of undergoing an ionic interactionor covalent reaction with the acrylic adhesive component of thecomposite pressure-sensitive adhesive.
 15. The compositepressure-sensitive adhesive of claim 14 wherein Y is a segmentcomprising at least 70 parts of at least one addition polymerizablemonomer of an alkyl acrylate, alkyl-methacrylate, or mixtures thereof,and greater than 0 to 30 parts of at least one polar monomer selectedfrom the group consisting of acrylic acid, methacrylic acid, itaconicacid, maleic acid, N-vinyl pyrrolidone, N-vinyl caprolactam, acrylamide,t-butyl acrylamide, N,N-(dimethylamino)ethyl acrylamide, N,N-dimethylacrylamide, N,N-dimethyl methacrylamide, N-vinylpyridine, and mixturesthereof.
 16. The composite pressure-sensitive adhesive of claim 14wherein Y comprises at least one functional group capable of undergoingan ionic interaction or covalent reaction with the acrylic adhesivecomponent of the composite pressure-sensitive adhesive, the functionalgroup being selected from the group consisting of carboxylic acid,sulfonic acid, phosphoric acid, hydroxy, lactam, lactone, amide, amine,anhydride, epoxide, isocyanate, carbamate, and mixtures thereof.
 17. Thecomposite pressure-sensitive adhesive of claim 14 wherein thecompatibilizer is selected from the group consisting ofstyrene-4-vinylpyridine copolymer, styrene-isooctyl acrylate copolymer,styrene-2-vinylpyridine copolymer, styrene-isooctyl acrylate-acrylicacid copolymer, styrene-(meth)acrylamide copolymer, styrene-acrylic acidcopolymer, styrene-N-(3-aminopropyl)methacrylamide copolymer,styrene-N,N-(dimethylamino)ethylacrylate copolymer,styrene-2-diethylaminostyrene copolymer, styrene-glycidylmetlacrylatecopolymner, styrene-2-hydroxyethylmethacrylate copolymer,styrene-N-vinylpyrrolidone copolymer, and mixtures thereof.
 18. Thecomposite pressure-sensitive adhesive of claim 14 wherein the acrylicadhesive and the polymer are arranged in alternating layers.
 19. Thecomposite pressure-sensitive adhesive of claim 18 comprising from 5 to100 layers, and optionally having an overall thickness below about 250μm.
 20. The composite pressure-sensitive adhesive of claim 14 having atleast one pressure-sensitive adhesive property from the group consistingof a room temperature shear strength greater than about 10,000 minutes,a peel adhesion greater than that of a substantially similar compositepressure-sensitive adhesive having no compatibilizer, and a 500-gramweight 70° C. shear strength greater than that of a substantiallysimilar composite pressure-sensitive adhesive having no compatibilizer.21. A pressure-sensitive adhesive article comprising a backing havingopposing surfaces, at least one of the surfaces bearing thereon thecomposite pressure-sensitive adhesive of claim
 14. 22. Thepressure-sensitive adhesive article of claim 14 wherein the backing isselected from the group consisting of an acrylic-containing foam,polychloroprene-containing foam, polyolefin-containing foam, andpolyurethane-containing foam.
 23. The composite pressure-sensitiveadhesive of claim 14 wherein the polymer component is apressure-sensitive adhesive.
 24. A composite pressure-sensitive adhesivecomprising: from about 95 to about 5 parts by weight of an acrylicpressure-sensitive adhesive; from about 5 to about 95 parts by weight ofan at least partially soluble styrene-containing polymer; and acompatibilizer present in the composite pressure-sensitive adhesive inan amount greater than 0 to below 5 parts by weight of the compositepressure-sensitive adhesive, the compatibilizer having a structureselected from the group consisting of (1) an acrylic adhesive-compatiblesegment and a polymer-compatible segment wherein at least a portion ofthe compatibilizer is present substantially throughout either theacrylic adhesive, the polymer, or both, and (2) an acrylicadhesive-reactive segment and a polymer-compatible segment wherein atleast a portion of the compatibilizer is present substantiallythroughout the polymer.